Molasses based alcohol distillery effluent is an extremely complex system and poses significant challenge in developing effective environmental remediation protocol. While use of this effluent in land application, to take advantage of nutrient value of constituent K, N and P have been reported in the literature and put in practice, effort have also been made to recover potassium from the effluent.
Reference may be made to U.S. Pat. No. 1,400,192, dated Dec. 13, 1921 by Whitaker M. C. which teaches about a process for precipitating potassium from distillery waste by using hexafluorosilicic acid as precipitant. However, use of hexafluorosilicic acid will lead to fluoride contamination in effluent stream necessitating additional input for environmental management of the effluent.
Reference may be made to section 5.1.6.3 of Indian Standard IS: 8032-1976 (reaffirmed 2003) “GUIDE FOR TREATMENT OF DISTILLERY EFFLUENTS”, which teaches about process for the recovery of potash from distillery spent wash. The process involves neutralization of spent wash followed by concentration and incineration to produce “spent wash coke” which on combustion produces ash. This ash is then leached with water. The leachate upon neutralisation with sulphuric acid and subsequent crystallization yields solid mixture of potassium sulphate and potassium chloride. However, this mixed salt is contaminated with ca. 5% sodium salts and may not meet the prevailing standards for use as fertiliser. Additionally, due to high probability of organic fouling and slag formation, evaporation and incineration performance is likely to be compromised on prolonged operation.
Reference may be made to Chinese patent no. 101781138 B dated Jul. 4, 2012 by Chen Y. et al. wherein potassium is selectively recovered from molasses based alcohol distillery waste through ion exchange process using ammonium modified natural zeolite. Subsequently the ion exchange column was eluted with solution of ammonium salt (viz., nitrate/sulphate chloride etc.) to release potassium is aqueous solution of corresponding ammonium salt solution. This solution is then concentrated to produce solid K—N fertiliser. However, in this process, during ion exchange ammonia is continually lost in K-depleted distillery waste, which will adversely affect process economics as well as quality of process effluent.
Reference may be made to European patent no. 2751028 dated Dec. 9, 2015 by Maiti P. et al. which teaches about a method for selectively precipitating potassium from aqueous solution, e.g., schoenite end liquor, using tartaric acid as precipitant. However, due to interaction of constituent solutes, particularly organics, straightforward implementation of this process results in lower K recovery and highly coloured and impure potash salt. Thus a need was felt to devise a safe and sustainable process for production of potassium salts of acceptable quality from alcohol distillery waste.